Pfizer’s investigational compound palbociclib (PD-0332991), an oral and selective inhibitor of cyclin dependent kinases (CDK) 4 and 6, has received Breakthrough Therapy designation by the FDA for the potential treatment of patients with breast cancer.

The Breakthrough Therapy designation was based on preliminary phase II data in this patient population. Interim data showed that women treated with the combination of palbociclib plus letrozole achieved a statistically significant improvement in median progression free survival (PFS) compared to women who received letrozole alone (26.1 months and 7.5 months, respectively).

“We appreciate the opportunity that Breakthrough Therapy designation provides to work closely with the FDA on the development of palbociclib,” said Dr. Mace Rothenberg, senior vice president of clinical development and medical affairs for Pfizer’s Oncology business unit. “Palbociclib is one example of Pfizer’s commitment to identifying and translating innovative science into meaningful new treatment options for cancer patients.”

Pfizer will continue to work with the FDA to better understand the implications of Breakthrough Therapy designation on the palbociclib development program and to generate evidence needed to support a potential regulatory submission. The FDA’s requirements for a potential submission have not yet been defined.

Pfizer has initiated a randomized, multi-center, double-blind phase III study (Study 1008) evaluating palbociclib in combination with letrozole versus letrozole alone as a first-line treatment for post-menopausal patients with ER+, HER2- locally advanced or metastatic breast cancer. Study 1008 is currently open and enrolling.